With the rapid development of world economy, energy and environmental problems have adversely affected the sustainable development of economy. Internal combustion engines are widely used, consume a large amount of gasoline and produce many harmful exhaust gases and particles. Therefore, it is urgent to develop internal combustion engines that have lower emissions and consume less energy.
Variable valve technology has attracted widespread attention of internal combustion engine research institutes and enterprises, as it improves the performance of internal combustion engines.
In addition, with the rapid increase of the number of internal combustion engines worldwide, losses in properties and people's lives due to traffic accidents grow year by year. Therefore, people are more and more concerned about vehicle safety and more and more countries list the auxiliary braking system as one of essential accessories of vehicles. However, at present, most auxiliary braking systems, e.g. eddy current retardant module and hydraulic retardant module, exhibit problems during operation.
For instance, brake parts overheat easily, the brake efficiency diminishes quickly, the controllability of braking ability is low, the vehicle tends to deviate while braking, and the brake system occupies too much space.
An auxiliary braking system could potentially solve all these problems.
Among current auxiliary braking systems of engines, the brake efficiency of a 720° C.A/cycle compression release engine brake system is the highest, but this system also has problems with brake power. Hence, it is urgent to develop a set of variable valve actuation system which can satisfy both 720° C.A/cycle actuation mode and 360° C.A/cycle compressor brake mode of an internal combustion engine.
At present, most practical variable valve actuation systems are equipped with distribution cams, have mechanical structures and are mainly divided into: 1) camshaft phase adjusting type, e.g. VVT system of TOYOTA and Vanos system of BMW; 2) staged variable valve lift type, e.g. VTEC system of Honda; 3) continuously variable valve lift type, e.g. Valvetronic system of BMW and CVVL system of Hyundai. These systems adjust the opening/closing timing and/or the maximum valve lift in each cylinder valve of an internal combustion engine.
Compared with cam-based variable valve actuation systems, cam-less systems can realize more flexible valve movements. Meanwhile, the structure of the cam-less systems is complicated, the cost is high and the reliability, durability and thermal expansion compensation control, etc. leave much to be desired. Cam-less systems can mainly be divided into electromagnetic type and electro-hydraulic type. Electro-hydraulic systems leave much to be desired in terms of movement accuracy control and valve lift adjustability. In contrast to electromagnetic systems, electro-hydraulic systems have higher valve flexibility, higher power density and higher layout flexibility, etc., and are the highest potential variable valve actuation systems. The electro-hydraulic systems mainly include common rail oil supply type and cam oil supply type.
Common rail oil supply systems are not equipped with distribution cams and adjust the opening/closing timing and maximum valve lift by controlling the open/close state of the electromagnetic valve and the actuation oil in the energy storage. Ford and Lucas, and others, conducted a study, but further studies are needed regarding cost, response speed, occupied space, etc.
With the increase of the cylinder number, single cylinder valve numbers and speeds of internal combustion engines, common rail oil supply systems still have the following defects: 1) the volume of common rail tube is high and the space layout is difficult; 2) too many electromagnetic valves with high speed and large flow rate are applied in the system, and materials and technical processes of electromagnetic valves decide their high cost. Therefore, the overall cost of the common rail oil supply systems is high. Therefore, also, it is more difficult to utilize traditional common rail oil supply electro-hydraulic variable valve actuators.
Through the combination of advantages of both mechanical and common rail oil supply systems, cam oil supply systems attract the wide attention of researchers and manufacturers, e.g. Multiair system of Fiat and VCM system of ABB. Such systems are equipped with a cam-plunger oil supply device instead of energy storage, occupy a smaller space and can synchronously adjust the opening/closing timing and valve lift. However, improvement is still required with regard to the following two aspects: first, the system needs more oil feeders and electromagnetic valves and its overall cost is high; second, the adjustable operating range of a valve affects the limit of oil supply and control devices, so it can neither realize the independent adjustment among the opening/closing timing and valve lift nor the 360° C.A/cycle valve operation process required by the auxiliary braking mode of an internal combustion engine.
To solve these problems of cam oil supply systems, a cam oil supply electro-hydraulic valve actuation system has been developed. This system adopts the cam-plunger oil supply pattern, the common rail pipe is removed, and few oil feeders are employed, which is favorable to the layout of the system space. However, such a system still has the following problems: 1) the system has too many electromagnetic valves and its cost is high; 2) the adjustable range of its valve actuator is restricted to the oil supply rate of its cam-plunger oil feeder; it is impossible to open the exhaust valve secondarily and change the 720° C.A/cycle mode of an internal combustion engine to the 360° C.A/cycle compressor brake mode, which restricts the extension of its functions.
To solve problems of cam oil supply electro-hydraulic valve actuation systems, a dual-mode fully variable valve actuation system has been developed. Through the use of drive-brake circulator and mode converter, this system has less electromagnetic valves, is driven by the internal combustion engine, and has the variable valve corresponding to the brake mode thereof. However, the dual-mode fully variable valve actuation system still has several defects: 1) as the two-position five-way valve of this system needs to the switched under the different pressure differences of each oil port and the pressure difference change of each oil port is extremely complicated, with the speed increase, the response time of the two-position five-way valve shall be shorter to ensure higher flow rate. Therefore, the two-position five-way valve has complicated structure and the processing cost thereof is high; 2) under the drive mode of the internal combustion engine, this system cannot close the valve when the oil feeder is working, which restricts the performance improvement of this system at idle or at the medium and low speed. While idling or the medium and low speed are common running conditions for urban vehicles, and the operation of the internal combustion engine under these running conditions basically decides the actual oil consumption and emission of the vehicles; 3) the structure of the drive-brake circulator is complicated, more external oil pipes are required, the system manufacturability is low, the production cost is high and its structural layout is difficult; 4) functions of various components of the system are mutually reliable, and the overall layout of the system and many components need to be changed according to different application requirements, which restricts the application range of the system.
To solve the defects of the cam oil supply electro-hydraulic valve actuation system and the dual mode fully variable valve actuation system, an intensive multifunctional variable valve actuation system has been developed in recent years, the electromagnetic valve structure is simplified and the valve can be closed under the drive mode of the internal combustion engine when the oil feeder supplies oil. However, this system still has the following two defects: 1) the cycle selector structure is complicated, more oil pipes are required, the system manufacturability is lower, its cost is higher and its layout is more different; 2) functions of various components of the system are mutually dependent, and the overall layout of the system and many components need to be changed according to different application requirements, which restricts the application scope of the system.